Optically sensitized light-sensitive material



United States Patent Int. (:1. Gil3c N08 US. Cl. 96-421 4 Claims ABSTRACT OF THE DISCLOSURE Dyes having the formula s X RSG c=o o=s as defined below are effective sensitizers for silver halide emulsions and electrophotographic layers. Their sensitization maximum is at 450 to 480 millimicrons with a sharp drop-off at longer wave lengths.

It has been known for a long time that the sensitivity of light-sensitive layers, especially silver halide emulsion layers, may be increased by adding substances which increase the spectral sensitivity range of the light-sensitive substances. Numerous substances which mainly belong to the class of cyanine dyes have been described for so sensitizing silver halide emulsion layers. These known substances, however, often have disadvantages in that their sensitizing effect is inadequate or that they cause the layer to be discolored, or adversely influence the photographic process itself. This applies in particular to special photographic processes or special photographic materials. The adsorption of the sensitizers on the silver halide should be so strong that the sensitizing effect will be impaired as little as possible by the other necessary additives such as wetting agents and emulsifiers, stabilizers, color couplers, dyes that can be bleached out, white toners, etc. 'It must also be possible to carry out sensitization under extreme conditions such as elevated temperature and high moisture-content. Furthermore, the sensitizing dyes must not increase the fog as is the case with the known basic cyanine dyes. For these reasons, there is considerable interest in finding new sensitizing dyes.

It is among the objects of the present invention to provide sensitizing dyes for spectrally sensitizing light-sensitive layers, especially silver halide emulsion layers, that do not suffer the above-mentioned disadvantages.

The object of the present invention is to provide sensitizing dyestuffs for sensitizing of light-sensitive layers, more especially silver halide emulsion layers, which have a particularly high sensitization intensity in the blue spectral region with a steepest possible decrease towards long wavelengths.

We now have found that light-sensitive materials, more especially silver halide layers, can be spectrally sensitized in excellent manner with cyanine dyes of the following formula wherein:

X=represents a sulfur or selenium atom;

R'=represents a sulfo-substituted or carboxyl-substituted,

saturated or unsaturated aliphatic group, advantageously with up to 5 carbon atoms;

R"==represents a saturated or unsaturated aliphatic group advantageously with up to 5 carbon atoms, and

R"'=represents (1) hydrogen, (2) a saturated or unsaturated aliphatic group, advantageously with up to 5 carbon atoms, which may be substituted, for example with sulfo, carboxyl, halogen such as chlorine, hydroxyl, alkoxy or the like, (3) aryl, advantageously phenyl, (4) cycloalkyl, advantageously cyclohexyl, or (5) heterocyclic ring, advantageously a saturated N- containing ring, such as morpholino, or piperidino, and the aryl, cycloalkyl or heterocyclic ring can be substituted, for example with sulfo or carboxyl groups.

The sensitizing dyes used according to the invention are advantageous in many respects, due to the fact that the radical R itself can be increased as desired. The sensitizing dyes of the present invention have a maximum of high intensity in the shortwave range of the visible spectrum, between approximately 450 and 480 me. With most of these dyes, the maximum is between 460 and 470 In,u.. The dyes are characterized by a steep flank on the long-wave side of the maximum. Consequently, photographic material sensitized with the dyes show 'an excellent safety in the dark-room.

The freedom from fogging and the stability under tropical conditions are excellent.

Dyes of the following formulae are, for example, suitable:

The aforementioned dyes can be prepared by known methods. The preparation of dye No. 2 is described in detail hereafter. The other sensitizing dyes are prepared in analogous manner.

PREPARATION OF DYE NO. 2

.(a) 80 g. of 2,5 -bis-(carbethoxymethylmercapto)- 1,3,4-thiadiazole are quaternized with 40 g. of dimethyl sulfate at 120 C. The oil which is obtained is washed with ethyl acetate and ether, is dissolved in 400 ml. of ethanol after adding 40 g. of 3-allyl rhodanine and then 25 ml. of triethylamine are added. The mixture is stirred for 15 minutes at 50 C., whereafter it is cooled and washed with ethanol. 42 g. of S-[S-carbethoxymethylcapto 3 methyl 2,3 dihydro 1,3,4 thiadiazolylidene-(2)]-3-allylrhodanine with a melting point of 165 to 167 C. are obtained.

(b) The ester obtained according to (a), (42 g.) is boiled with 800 ml. of n-propanol, 350 ml. of H and 60 ml. of 2 N=NaOH for 3 minutes. It is then acidified with 2 N=HC1 and cooled. The precipitated dye is recrystallized twice from glacial acetic acid. 25 g. of the dye No. 2 with a melting point of 197 to 199 C. are obtained.

The other sensitizing dyes have melting points as follows:

Dyestuff No.: M.P. C.)

The preparation of photographic silver halide emulsions substantially comprises three steps:

(1) Precipitation of the silver halide in the presence of a protective colloid and physical ripening.

(2) Removal from the emulsion of excess watersoluble salts introduced during precipitation, generally by washing, and

(3) Chemical ripening or after-ripening, which serves to impart the desired sensitivity to the emulsion.

The sensitizing dyes according to the present invention can be used in any silver halide emulsions. Suitable silver halides are silver chloride, silver bromide or mixtures thereof, if desired containing a small amount of silver iodide up to 10 mole percent. The silver halides may be dispersed in the usual hydrophilic compounds, for example, carboxymethylcellulose, polyvinyl alcohol, polyvinyl pyrrolidone, alginic acid and its salts, esters, or amides or preferably gelatin.

The sensitizing dyes to be used according to the present invention are advantageously added to the photographic emulsion before the chemical ripening or before casting. The methods employed for this are generally known to persons skilled in this art. The sensitizing dyes are generally incorporated in the emulsion in the form of solutions, e.g., in alcohol or mixtures of alcohol and Water. The solvents must, of course, be compatible with gelatin and must not have any adverse effects on the photographic properties of the emulsion. Water, methanol or mixtures thereof are generally used as solvents. The quantity of sensitizing dye added may vary within wide limits, e.g., between 2 and 200 mg. preferably between 10 and mg. per kg. of the silver halide emulsion. The concentration of dye may be adapted to the particular requirements, depending on the type of emulsion, the desired sensitizing effect, etc. The most suitable concentration for any given emulsion can easily be determined by the usual tests employed in the art of emulsion making.

The emulsions may also contain chemical sensitizers, e.g., reducing agents such as stannous salts, polyamines such as diethylentriamine, or sulfur compounds as described in US. Pat. No. 1,574,944. Furthermore, salts of noble metals, such as ruthenium, rhodium, palladium, iridium, platinum or gold may be contained in the emulsions for chemcial sensitization, as described in the article by R. Koslowsky, Z. Wiss. Phot. 46, -72 (1951). The emulsions may also contain, as chemical sensitizers, polyalkylene oxides, especially polyethylene oxide and derivatives thereof.

The emulsions according to the present invention may contain the usual stabilizers such as homopolar or salttype compounds of mercury with aromatic or heterocyclic rings, such as mercaptotriazoles, simple mercury salts, sulfonium mercury double salts and other mercury compounds. Other suitable stabilizers are azaindenes, especially tetraor pentaazaindenes, in particular those that are substituted with hydroxyl or amino groups. Compounds of this type are described in the article by Birr, Z. Wiss. Phot. 47, 2-58 (1952). Other suitable stabilizers include heterocyclic mercapto compounds, e.g., phenylmercaptotetrazole, quaternary benzothiazole derivatives and benzotriazole.

The emulsions may be hardened in the usual manner, for example, with formaldehyde or by use of halogen-substituted aldehydes which contain a carboxyl group, e.g., mucobromic acid, diketones, methanesulfonic acid esters and dialdehydes.

The emulsions according to the invention may be used for all sorts of different photographic processes, for example, for copying materials, for reproduction photography, for X-ray films, for materials which are suitable for use in the silver salt diffusion process, for color photographic materials for the silver dye bleaching process, etc.

The sensitizers used according to the invention are in addition suitable for the spectral sensitization of electrophotographic layers, advantageously those layers which contain photoconductive zinc oxide distributed in an insulating binder.

EXAMPLE 30 mg. of the sensitizing dye No. 2 are added to a conventional photographic gelatino-silver chlorobromide emulsion, which is chemically sensitized with gold-III- chloride and is stabilized by addition of 7 ml. of a 1% methanolic solution of phenylmercaptotetrazole. The emulsion is applied in the usual manner onto a baryta-coated paper support and dried. The light-sensitive layer is exposed behind a stepped wedge; development takes place for 1 /2 minutes in a developer having the following composition:

Water cc 1000 p-Methylaminophenol g 1 Hydroquinone ng 3 Anhydrous sodium sulfite g 13 Anhydrous soda g 26 Potassium bromide g l The stepped wedge which is obtained shows the excellent sensitizing action of the dye. The sensitization maximum is at 465 m Equally good results are obtained if the sensitizing dye No. 2 is replaced by similar quantities of other sensitizing dyes of the invention.

The sensitizing action is not impaired if color couplers, e.g. yellow couplers, are added to the above emulsion.

The sensitization intensity and the stability under tropical conditions are excellent. Equally good results are also obtained by using other emulsions, such as silver bromide emulsions with a particularly steep gradation.

What is claimed is:

1. In a light sensitive photographic material in which the light sensitive composition is spectrally sensitized with a dye, the improvement wherein said dye is a compound of the formula:

wherein:

2. The composition of claim 1 in which the light-sensitive material is a silver halide emulsion.

3. The composition of claim 2, wherein the emulsion is a silver chloride or silver chlorobromide emulsion.

4. The composition of claim 2, wherein the sensitizing compound has the formula:

References Cited UNITED STATES PATENTS 5/1968 Riester et a1 96102 0 NORMAN G. TORCHIN, Primary Examiner A. T. SURO PICO, Assistant Examiner US. Cl. X.R. 96l04 

